Apparatus and method for measuring surface topography optically

ABSTRACT

An apparatus is described for determining surface topography of a three-dimensional structure. The apparatus can include a probe and an illumination unit configured to output a plurality of light beams. In many embodiments, the apparatus includes a light focusing assembly. The light focusing assembly can receive and focus each of a plurality of light beams to a respective external focal point. The light focusing assembly can be configured to overlap the plurality of light beams within a focus changing assembly in order to move the external focal points along a direction of propagation of the light beams. The apparatus can include a detector having an array of sensing elements configured to measure a characteristic of each of a plurality of light beams returning from the illuminated spots and a processor coupled to the detector and configured to generate data representative of topography of the structure based on the measured characteristic.

CROSS-REFERENCE

This application is a continuation of U.S. application Ser. No.15/811,365, filed Nov. 13, 2017, which is a continuation of U.S.application Ser. No. 15/220,336, filed Jul. 26, 2016, now U.S. Pat. No.9,844,427, issued Dec. 19, 2017, which is a continuation of U.S.application Ser. No. 14/323,215, filed Jul. 3, 2014, now U.S. Pat. No.9,439,568, issued Sep. 13, 2016, each of which is incorporated herein byreference in their entirety.

BACKGROUND

A variety of approaches have been developed for measuring surfacetopography optically. For example, optical systems and methods have beendeveloped and employed that can be used to optically measure surfacetopography of a patient's teeth. The measured surface topography of theteeth can be used, for example, to design and manufacture a dentalprosthesis and/or to determine an orthodontic treatment plan to correcta malocclusion.

One technique for measuring surface topography optically employs lasertriangulation to measure distance between a surface of the tooth and anoptical distance probe, which is inserted into the oral cavity of thepatient. Surface topography measured via laser triangulation, however,may be less accurate than desired due to, for example, sub-optimalreflectivity from the surface of the tooth.

Other techniques for measuring surface topography optically, which areembodied in CEREC-1 and CEREC-2 systems commercially available fromSiemens GmbH or Sirona Dental Systems, utilize the light-section methodand phase-shift method, respectively. Both systems employ a speciallydesigned hand-held probe to measure the three-dimensional coordinates ofa prepared tooth. Both of these approaches, however, require a specificcoating (i.e. measurement powder and white-pigments suspension,respectively) to be deposited to the tooth. The thickness of the coatinglayer should meet specific, difficult to control requirements, whichleads to inaccuracies in the measurement data.

In yet another technique, mapping of teeth surface is based on physicalscanning of the surface by a probe and by determining the probe'sposition, e.g., by optical or other remote sensing means.

U.S. Pat. No. 5,372,502 discloses an optical probe for three-dimensionalsurveying. Various patterns are projected onto the tooth or teeth to bemeasured and corresponding plurality of distorted patterns are capturedby the optical probe. Each captured pattern provides refinement of thetopography.

SUMMARY

Apparatus and methods for optically determining surface topography ofthree-dimensional structures are provided. In many embodiments, anapparatus for optically determining surface topography includes a lightfocusing assembly operable to vary focal depth of light beams incidentupon the three-dimensional structure (e.g., a patient's dentition) beingmeasured. The light focusing assemblies disclosed herein providevariation of focal depth with minimal or no moving parts, which providessmaller, faster, and more compact optics.

In one aspect, an apparatus is described for determining surfacetopography of a three-dimensional structure. In many embodiments, theapparatus includes a light focusing assembly. The light focusingassembly can be configured to overlap the light beams within a focuschanging assembly in order to move external focal points of the lightbeams along a direction of propagation of the light beams.Characteristics of light reflected from the measured structure can bemeasured. The measured characteristics can be used to generate datarepresentative of topography of the structure.

In another aspect, an apparatus is described for determining surfacetopography of a three-dimensional structure. In many embodiments, theapparatus includes a light focusing assembly. The light focusingassembly can include a convergent lens and a divergent lens. Theseparation between the convergent lens and divergent lens can be variedin order to displace external focal points of the light beams along adirection of propagation of the light beams. Characteristics of lightreflected from the measured structure can be measured. The measuredcharacteristics can be used to generate data representative oftopography of the structure.

Other objects and features of the present invention will become apparentby a review of the specification, claims, and appended figures.

INCORPORATION BY REFERENCE

All publications, patents, and patent applications mentioned in thisspecification are herein incorporated by reference to the same extent asif each individual publication, patent, or patent application wasspecifically and individually indicated to be incorporated by reference.

BRIEF DESCRIPTION OF THE DRAWINGS

The novel features of the invention are set forth with particularity inthe appended claims. A better understanding of the features andadvantages of the present invention will be obtained by reference to thefollowing detailed description that sets forth illustrative embodiments,in which the principles of the invention are utilized, and theaccompanying drawings of which:

FIGS. 1A and 1B schematically illustrate, by way of a block diagram, anapparatus in accordance with many embodiments (FIG. 1B is a continuationof FIG. 1A);

FIG. 2A is a top view of a probing member, in accordance with manyembodiments;

FIG. 2B is a longitudinal cross-section through line II-II in FIG. 2A,depicting exemplary rays passing therethrough;

FIG. 3 illustrates a telescopic light focusing assembly, in accordancewith many embodiments;

FIG. 4 illustrates a light focusing assembly with a variable opticalpower element, in accordance with many embodiments;

FIG. 5 illustrates a light focusing assembly with a focus changing lensgroup, in accordance with many embodiments;

FIG. 6 is a simplified block diagram presenting acts of a method fordetermining surface topography of a three-dimensional structure, inaccordance with many embodiments;

FIG. 7 illustrates a telescopic light focusing assembly, in accordancewith many embodiments;

FIG. 8 illustrates a compact light focusing assembly, in accordance withmany embodiments;

FIG. 9 illustrates a compact light focusing assembly and an opticalprobe, in accordance with many embodiments; and

FIG. 10 is a simplified block diagram presenting acts of a method fordetermining surface topography of a three-dimensional structure, inaccordance with many embodiments.

DETAILED DESCRIPTION

In many embodiments, an apparatus for optically determining surfacetopography includes a light focusing assembly that is configured tocontrollably vary focal depth of light beams that are projected towardsa three-dimensional structure (e.g., a patient's dentition) beingmeasured. In contrast to conventional approaches that employ substantialmovement of optical components, the light focusing assemblies disclosedherein employ few if any moving parts, thereby being smaller, faster,and more compact. Furthermore, the apparatus and methods disclosedherein for optically determining surface topography can be used to varythe focal depth of the light beams while maintaining telecentricity.Telecentric optics produce constant image magnification independent ofthe object distance over a defined telecentric range, and can thereforebe advantageous for improving the accuracy of optical measurementsystems.

The apparatus and methods described herein can be used to take opticalmeasurements of the surfaces of any suitable three-dimensionalstructure. In many embodiments, optical measurements are taken togenerate data representing the three-dimensional surface topography of apatient's dentition. The data can be used, for example, to produce athree-dimensional virtual model of the dentition that can be displayedand manipulated. The three-dimensional virtual models can be used to,for example, define spatial relationships of a patient's dentition thatare used to create a dental prosthesis (e.g., a crown or a bridge) forthe patient. The surface topography data can be stored and/ortransmitted and/or output, such as to a manufacturing device that can beused to, for example, make a physical model of the patient's dentitionfor use by a dental technician to create a dental prosthesis for thepatient.

In one aspect, an apparatus is provided for determining surfacetopography of a three-dimensional structure. The apparatus can include aprobe, such as a probing member sized for insertion into the intraoralcavity. The apparatus can include an illumination unit configured tooutput a plurality of light beams. The light beams can propagate towardthe structure along an optical path through the probe to generateilluminated spots on the structure. The surface of the structurereflects the incident light beams thereby producing a plurality ofreturning light beams. The apparatus can further include a detectorconfigured to measure a characteristic of each of the plurality of lightbeams returning from the illuminated spots. Such characteristics caninclude, for example, intensity, wavelength, polarization, phase shift,interference, and/or dispersion of the returning light beams. Anydescription herein relating to light intensity can also be applied toother suitable characteristics of light, and vice-versa. Themeasurements of the characteristic(s) can be used to detect whether theincident light beams are focused on the surface of the structure andthereby determine the distance between the optical probe and thethree-dimensional structure.

A processor can be coupled to the detector to generate datarepresentative of the topography of the structure based on measuredcharacteristics of each of a plurality of light beams returning from theilluminated spots. For example, the surface topography of the structurecan be determined based on measuring the intensities of the returninglight beams. In many embodiments, the apparatus is configured such thatthe intensity of any particular light beam returning from the structureis maximized when the incident light beam is focused on the surface ofthe structure, thus relating the magnitude of the intensity signal tothe focal depth of the apparatus. Consequently, the relative depth ofeach point on the surface of the structure can be determined by scanningthe light beams through a range of focal depths and identifying thefocal depth at which the peak intensity signal is obtained. The surfacetopography of the structure can thus be determined by repeating thisprocess for each point on the structure.

As another example, the surface topography can be determined by usingspatial frequency analysis to identify which regions of the structureare in focus. In many embodiments, focused regions will contain higherspatial frequencies than out of focus regions. Accordingly, a distancebetween the probe and a specified region on the structure for aparticular position and orientation of the probe relative to thestructure can be determined by identifying when the spatial frequenciesof the region are maximized. This approach can be applied to determinethe surface topography of structures having spatial details.

In order to scan the focus the light beams through the range of focaldepths, the apparatus can include a light focusing assembly. The lightfocusing assembly can be configured to focus each of a plurality of thelight beams to a respective external focal point. The light beams mayemanate from the probe at a location disposed between the respectiveexternal focal point and the light focusing assembly. To scan the focusof the light beams through the range of focal depths, the light focusingassembly can also be configured to overlap a plurality of the lightbeams within a focus changing assembly. The focus changing assembly canbe operated to displace the external focal points along a direction ofpropagation of the light beams.

Many configurations are possible for the light focusing assembly andfocus changing assembly. For example, at a least a portion of the focuschanging assembly can be located at a back focal length of an objectivelens of the light focusing assembly in order to inhibit changes inspacing between external focal points of the plurality of light beamswhen the external focal points move along the direction of propagationof the light beams. Alternatively or in combination, the focus changingassembly can be located along optical paths of the plurality of lightbeams such that a majority of the plurality of light beams overlaps withother light beams of the plurality along at least a portion of the focuschanging assembly in order to inhibit changes in spacing betweenexternal focal points of the plurality of light beams when the externalfocal points move along the direction of propagation of the light beams.Each of the plurality of light beams may comprise a substantiallycollimated configuration upon entering the focus changing assembly. Thefocus changing assembly can similarly adjust each of the plurality oflight beams to a convergent configuration, a collimated configuration,or a divergent configuration upon exiting the focus changing assembly inorder to move the external focal points along the direction ofpropagation of the light beams. For instance, the focus changingassembly may move the external focal points at least 10 mm.

In many embodiments, the light focusing assembly includes one or moreimage space lenses and one or more object space lenses, with the focuschanging assembly located along an optical path between the one or moreimage space lenses and the one or more object space lenses. The one ormore object space lenses may comprise a telecentric lens and at least aportion of the focus changing assembly may be located at a back focallength of the telecentric lens. The one or more image space lenses maycomprise a focal length and location arranged to overlap andsubstantially collimate the plurality of light beams passing through thefocus changing assembly.

In many embodiments, the focus changing assembly includes a variableoptical power element operable to move the external focal points withoutmovement of the variable optical power element. The variable opticalpower element can be operated at a suitable frequency so as to oscillateseparation between the external focal points and the probe by a desiredrange. For example, the variable optical power element may be operableto oscillate separation between the external focal points and the probeby at least 10 mm at a frequency greater than 10 Hz, or at a frequencyfrom approximately 50 Hz to approximately 100 Hz.

Alternatively or in combination, the focus changing assembly cancomprise a focus changing group of lenses in which the separationbetween lenses is varied to displace the external focal points throughthe range of focal depths. For example, the focus changing group oflenses can include a divergent lens and a convergent lens, withseparation between the divergent lens and convergent lens being variedto displace the external focal points. In many embodiments, a change inseparation between the lenses of the focus changing group of lensesresults in a change in separation between the external focal points andthe probe that is greater than the change in separation between thelenses. For example, the focus changing assembly can move the externalfocal points over a distance that is at least two times greater than acorresponding distance moved by at least a portion of the focus changingassembly. The change in separation between the lenses of thefocus-changing group may result in a change in separation between theexternal focal points and the probe of at least 5 times or approximately7.5 times the change in separation between the lenses of the focuschanging group of lenses. Additionally, in many embodiments, thevariable optical power element or the focus changing group lenses isoperable to oscillate separation between the external focal points andthe probe by a suitable distance and at a suitable frequency. Forinstance, the focus changing group of lenses may be operable tooscillate separation between the external focal points and the probe byat least 10 mm at a frequency greater than 10 Hz, or by at least 15 mmat a frequency from approximately 10 Hz to approximately 100 Hz.

In another aspect, a method is provided for determining surfacetopography of a three-dimensional structure. The method includesgenerating illuminated spots on the structure using a light focusingassembly to receive and focus each of a plurality of light beams to arespective external focal point external to a probe sized to be insertedinto an intraoral cavity of a patient. The light focusing assembly canbe operated to overlap each of the plurality of light beams within afocus changing assembly. The focus changing assembly can be operated todisplace the external focal points along a direction of propagation ofthe plurality of light beams. The surface of the structure can reflectthe light from the illuminated spots thereby producing a plurality ofreturning light beams. A characteristic of each of a plurality of lightbeams returning from the illuminated spots can be measured. Based on themeasured characteristics, data representative of topography of thestructure can be generated, as previously described herein.

In another aspect, an apparatus is provided for determining surfacetopography of a three-dimensional structure. The apparatus can include aprobe, such as a probing member sized for insertion into the intraoralcavity. The apparatus can include an illumination unit configured tooutput an array of light beams. The light beams can propagate toward thestructure along an optical path through the probe to generateilluminated spots on the structure. The surface of the structure canreflect the light from the illuminated spots thereby producing aplurality of returning light beams. The apparatus can further include adetector configured to measure a characteristic of each of the pluralityof light beams returning from the illuminated spots. A processor can becoupled to the detector to generate data representative of thetopography of the structure based on measured characteristics of each ofa plurality of light beams returning from the illuminated spots, aspreviously described herein. The characteristic may comprise anintensity, for example.

To scan the focus of the light beams through the range of focal depths,the apparatus can include a light focusing assembly that includes aconvergent lens and a divergent lens. The light focusing assembly can beconfigured to overlap each of the plurality of light beams to a systemaperture disposed between the light focusing assembly and a locationwhere the light beams emanate from the probe. The light focusingassembly can be operable to vary separation between the convergent lensand divergent lens to vary separation between the probe and an externalfocal point for each of the plurality of the light beams. In manyembodiments, a change in separation between the convergent lens and thedivergent lens results in a change in separation between the externalfocal points and the probe that is greater than the change in separationbetween the convergent lens and the divergent lens (e.g., at least 2times or at least 4 times greater). In many embodiments, the divergentlens is disposed between the convergent lens and the system aperture.The apparatus can further include a telecentric lens disposed on theoptical path between the system aperture and the external focal points.

In another aspect, a method is provided for determining surfacetopography of a three-dimensional structure. The method includesgenerating an array of light beams that propagate along an optical pathto form illuminated spots on the structure. The optical path passesthrough a convergent lens, a divergent lens, and a probe sized to beinserted into an intraoral cavity of a patient. The divergent lens canbe disposed between the convergent lens and a location where the lightbeams emanate from the probe. The surface of the structure reflectslight from the illuminated spots thereby producing a plurality ofreturning light beams. A characteristic of each of a plurality lightbeams returning from the structure is measured. Based on the measuredcharacteristic, data representative of topography of the structure isgenerated, as previously described herein. To scan the focus of thelight beams through the range of focal depths, the separation betweenthe convergent lens and the divergent lens is varied to vary separationbetween the probe and respective external focal points of each of aplurality of the light beams.

Turning now to the drawings, in which like numbers designate likeelements in the various figures, FIGS. 1A and 1B illustrate an apparatus20 for measuring surface topography optically. The apparatus 20 includesan optical device 22 coupled to a processor 24. The illustratedembodiment is particularly useful for measuring surface topography of apatient's teeth 26. For example, the apparatus 20 can be used to measuresurface topography of a portion of the patient's teeth where at leastone tooth or portion of tooth is missing to generate surface topographydata for subsequent use in design and/or manufacture of a prosthesis forthe patient (e.g., a crown or a bridge). It should be noted, however,that the invention is not limited to measuring surface topography ofteeth, and applies, mutatis mutandis, also to a variety of otherapplications of imaging of three-dimensional structure of objects (e.g.,for the recordal of archeological objects, for imaging of athree-dimensional structure of any suitable item such as a biologicaltissue, etc.).

The optical device 22 includes, in the illustrated embodiment, a lightsource 28 (e.g., a semiconductor laser unit) emitting a light, asrepresented by arrow 30. The light passes through a polarizer 32, whichcauses the light passing through the polarizer 32 to have a certainpolarization. The light then enters into an optic expander 34, whichincreases the diameter of the light beam 30. The light beam 30 thenpasses through a module 38, which can, for example, be a grating or amicro lens array that splits the parent beam 30 into a plurality oflight beams 36, represented here, for ease of illustration, by a singleline.

The optical device 22 further includes a partially transparent mirror 40having a small central aperture. The mirror 40 allows transfer of lightfrom the light source 28 through the downstream optics, but reflectslight travelling in the opposite direction. It should be noted that inprinciple, rather than a partially transparent mirror, other opticalcomponents with a similar function may be used (e.g., a beam splitter).The aperture in the mirror 40 improves the measurement accuracy of theapparatus. As a result of this mirror structure, the light beams producea light annulus on the illuminated area of the imaged object as long asthe area is not in focus. The annulus becomes a sharply-focusedilluminated spot when the light beam is in focus relative to the imagedobject. Accordingly, a difference between the measured intensity whenout-of-focus and in-focus is larger. Another advantage of a mirror ofthis kind, as opposed to a beam splitter, is that internal reflectionsthat occur in a beam splitter are avoided, and hence the signal-to-noiseratio is greater.

The optical device 22 further includes confocal optics 42, typicallyoperating in a telecentric mode, relay optics 44, and an endoscopicprobe member 46. In many embodiments, the confocal optics 42 isconfigured to avoid distance-introduced magnification changes andmaintain the same magnification of the image over a wide range ofdistances in the Z direction (the Z direction being the direction ofbeam propagation). In many embodiments, the confocal optics 42 aretelecentric, and can even be double telecentric. Double telecentricconfocal optics (telecentric in both image space and object space) canprovide improved optical measurement accuracies compared tonon-telecentric optics or optics telecentric in image space or objectspace only. Exemplary embodiments of a light focusing assembly that canbe included in the confocal optics 42 are described below. In manyembodiments, the relay optics 44 is configured to maintain a certainnumerical aperture of the light beam's propagation.

The endoscopic probe member 46 can include a light-transmitting medium,which can be a hollow object defining within it a light transmissionpath or an object made of a light transmitting material (e.g., a glassbody or tube). The light-transmitting medium may be rigid or flexible(e.g., fiber optics). In many embodiments, the endoscopic probe member46 includes a mirror of the kind ensuring total internal reflection anddirecting the incident light beams towards the patient's teeth 26. Theendoscope 46 thus emits a plurality of incident light beams 48 impingingon to the surface of the patient's teeth 26.

The incident light beams 48 form an array of light beams arranged in anX-Y plane, relative to a Cartesian reference frame 50, and propagatingalong the Z-axis. When the incident light beams 48 are incident upon anuneven surface, resulting illuminated spots 52 are displaced from oneanother along the Z-axis, at different (X_(i),Y_(i)) locations. Thus,while an illuminated spot 52 at one location may be in focus for a givenfocal length produced by the confocal optics 42, illuminated spots 52 atother locations may be out-of-focus. Therefore, the light intensity ofthe returned light beams of the focused spots will be at its peak, whilethe light intensity at other spots will be off peak. Thus, for eachilluminated spot, a plurality of measurements of light intensity aremade at different positions along the Z-axis and for each of such(X_(i),Y_(i)) locations, typically the derivative of the intensity overdistance (Z) will be made, and the Z_(i) distance yielding the maximumderivative, Z₀, will be the in-focus distance. As pointed out above,where, as a result of use of the punctured mirror 40, the incident lightforms a light disk on the surface when out of focus and asharply-focused light spot only when in focus, the distance derivativewill be larger when approaching in-focus position thus increasingaccuracy of the measurement.

The light reflected from each of the illuminated spots 52 includes abeam travelling initially in the Z axis in the opposite direction of theoptical path traveled by the incident light beams. Each returned lightbeam 54 corresponds to one of the incident light beams 36. Given theasymmetrical properties of mirror 40, the returned light beams 54 arereflected in the direction of a detection assembly 60. The detectionassembly 60 includes a polarizer 62 that has a plane of preferredpolarization oriented normal to the polarization plane of polarizer 32.The returned polarized light beam 54 pass through imaging optics 64,typically a lens or a plurality of lenses, and then through an array ofpinholes 66. Each returned light beam 54 passes at least partiallythrough a respective pinhole of the array of pinholes 66. A sensor array68, which can be a charge-coupled device (CCD) or any other suitableimage sensor, includes a matrix of sensing elements. In manyembodiments, each sensing element represents a pixel of the image andeach sensing element corresponds to one pinhole in the array 66.

The sensor array 68 is connected to an image-capturing module 80 of theprocessor unit 24. The light intensity measured by each of the sensingelements of the sensor array 68 is analyzed, in a manner describedbelow, by the processor 24. Although the optical device 22 is depictedin FIGS. 1A and 1B as measuring light intensity, the device 22 can alsobe configured to measure other suitable characteristics (e.g.,wavelength, polarization, phase shift, interference, dispersion), aspreviously described herein.

The optical device 22 includes a control module 70 that controlsoperation of the light source 28 and/or a motor 72. In many embodiments,the motor 72 is drivingly coupled with the confocal optics 42 so as toscan the focus of the light beams through a range of focal depths alongthe Z-axis. In a single sequence of operation, the control unit 70induces motor 72 to reconfigure the confocal optics 42 to change thefocal plane location and then, after receipt of a feedback signal thatthe location has changed, the control module 70 induces the light source28 to generate a light pulse. The control module 70 synchronizes theoperation of the image-capturing module 80 with the operation of theconfocal optics 42 and the light source 28 during acquisition of datarepresentative of the light intensity (or other characteristic) fromeach of the sensing elements. Then, in subsequent sequences, theconfocal optics 42 causes the focal plane to change in the same mannerand intensity data acquisition continues over a range of focal lengths.

The intensity data is processed by the processor 24 per processingsoftware 82 to determine relative intensity in each pixel over theentire range of focal planes of confocal optics 42. As explained above,once a certain light spot is in focus on the three-dimensional structurebeing measured, the measured intensity of the returning light beam willbe maximal. Thus, by determining the Z_(i) corresponding to the maximallight intensity or by determining the minimum derivative of the lightintensity, for each pixel, the relative in-focus focal length along theZ-axis can be determined for each light beam. Thus, data representativeof the three-dimensional topography of the external surfaces of theteeth is obtained. A resulting three-dimensional representation can bedisplayed on a display 84 and manipulated for viewing (e.g., viewingfrom different angles, zooming-in or out) by a user control module 85(e.g., utilizing a computer keyboard, mouse, joystick, or touchscreen).In addition, the data representative of the surface topography can betransmitted through an appropriate data port such as, for example, amodem 88 or any suitable communication network (e.g., a telephonenetwork) to a recipient (e.g., to an off-site CAD/CAM apparatus).

By capturing, in this manner, relative distance data between the probeand the structure being measured from two or more angular locationsaround the structure (e.g., in the case of a teeth segment, from thebuccal direction, lingual direction and/or optionally from above theteeth), an accurate three-dimensional representation of the structurecan be generated. The three-dimensional data and/or the resultingthree-dimensional representation can be used to create a virtual modelof the three-dimensional structure in a computerized environment and/ora physical model fabricated in any suitable fashion (e.g., via acomputer controlled milling machine, a rapid prototyping apparatus suchas a stereolithography apparatus).

As already pointed out above, a particular and preferred application isimaging of a segment of teeth having at least one missing tooth or aportion of a tooth. The resulting three-dimensional surface topographydata can, for example, be used for the design and subsequent manufactureof a crown or any other prosthesis to be fitted into this segment.

Referring now to FIGS. 2A and 2B, a probing member 90 is illustrated inaccordance with many embodiments. In many embodiments, the probingmember 90 forms at least a portion of the endoscope 46. The probingmember 90 may be sized to be at least partially inserted into apatient's intraoral cavity. The probing member 90 can be made of a lighttransmissive material (e.g., glass, crystal, plastic, etc.) and includesa distal segment 91 and a proximal segment 92, tightly glued together inan optically transmissive manner at 93. A slanted face 94 is covered bya reflective mirror layer 95. A transparent disk 96 (e.g., made ofglass, crystal, plastic, or any other suitable transparent material)defining a sensing surface 97 is disposed along the optical path distalto the mirror layer 95 so as to leave an air gap 98 between thetransparent disk 96 and the distal segment 91. The transparent disk 96is fixed in position by a holding structure (not shown). Three lightrays 99 are represented schematically. As can be seen, the light rays 99reflect from the walls of the probing member 90 at an angle in which thewalls are totally reflective, reflect from the mirror layer 95, and thenpropagate through the sensing face 97. The light rays 99 are focused ona focusing plane 100, the position of which can be changed by theconfocal optics 42.

In many embodiments, the confocal optics 42 includes a telescopic lightfocusing assembly. The telescopic light focusing assembly is configuredand operable to scan the focal points of the light beams through a rangeof focal depths. Scanning the focal points through a range of focaldepths is accomplished in order to determine the in-focus distance foreach of the light beams relative to the surface being measured, aspreviously described herein.

FIG. 3 illustrates a telescopic light focusing assembly 200, inaccordance with many embodiments, that can be included in the confocaloptics 42. The light focusing assembly 200 is configured and operable toscan the focal points of a plurality of light beams (e.g., atwo-dimensional array of light beams) through a range of focal depths.The light focusing assembly 200 can include an image space lens group202 and an object space lens group 204. The light focusing assembly 200can be configured and operable to focus the light beams on to anexternal focal plane 206 (e.g., external to the endoscopic probe member46) and controllably scan the location of the external focal plane 206relative to the endoscopic probe member 46. The light beam chief raysmay cross the optical axis at the back focal plane of the object spacegroup 204 that is disposed between the image space group 202 and theobject space group 204. A system aperture 208 may be situated at or nearthe back focal plane. An aperture stop (APS) 210 may be positioned at ornear the system aperture 208. In many embodiments, the aperture stop 210includes a circular opening in a physical light blocking plane and isused to define the beam width and, hence, the Numerical Aperture (NA) ofthe optical system.

Each of the image space lens group 202 and object space lens group 204can each include one or more lenses. For example, in many embodiments,each of the image space lens group 202 and object space lens group 204have a single convergent lens (e.g., a biconvex lens). “Lens” may beused herein to refer an element having a single lens or multiple lenses(e.g., doublet or triplet lenses).

To change the relative distance between the endoscopic probe member 46and the external focal plane 206, the distance between the object spacelens group 204 and the image space lens group 202 can be changed, forexample, by a mechanism driven by the motor 72. The mechanism maydisplace one or more of the object space lens group 204 or image spacelens group 202 along the direction of beam propagation along the opticalaxis of the optical system, also called the symmetry axis. By changingthe distance between the object space lens group 204 and the image spacelens group 202, the external focal plane 206 is displaced along thedirection of beam propagation. The external focal plane 206 can bedisplaced to any suitable position, such as to a near focus position212, an intermediate focus position 214, or a far focus position 216, bymoving the object space lens group 204 along the symmetry axis.

In a telescopic light focusing assembly, telecentricity may becompromised when the external focal plane 206 is displaced due todisplacement of the object space lens group 204 relative to the APS 210.The displacement of the object space lens group 204 relative to the APS210 results in the light rays being refracted by different portions ofthe object space lens group 204.

FIG. 4 illustrates a light focusing assembly 220, in accordance withmany embodiments, that can be included in the confocal optics 42. Thelight focusing assembly 220 can include an image space lens group 202,an object space lens group 204, and a focus changing assembly 222disposed along an optical path between the image and object space lensgroups, such as at or near a system aperture 208. At least one lenselement of the image space lens group 202 or object space lens group 204may be a telecentric lens. One or more optical components of the lightfocusing assembly 220 can be configured to overlap the plurality oflight beams within the focus changing assembly 222. For instance, atleast one lens element of the image space lens group 202 may comprise afocal length and location arranged to overlap and substantiallycollimate the light beams passing through the focus changing assembly222.

The light focusing assembly 220 can be operable to displace the externalfocal plane 206 without moving the object space lens group 204 relativeto the image space lens group 202. The external focal plane 206 can bedisplaced along the symmetry axis (e.g., to near, intermediate, and farfocus positions) by varying the optical power of the focus changingassembly 222. Accordingly, the light focusing assembly 220 can maintaintelecentricity and magnification even when shifting the location of theexternal focal plane 206. In many embodiments, the positioning andconfiguration of the focus changing assembly inhibits changes in spacingbetween external focal points of the external light beams when theexternal focal points are moved along the direction of propagation ofthe light beams. For example, the focus changing assembly 222 can belocated at or near a back focal length of an objective lens (e.g.,object space lens group 204) of the light focusing assembly 220.Alternatively or in combination, the focus changing assembly 222 can belocated along the optical paths of the plurality of light beams suchthat a majority of the plurality of light beams overlap other lightbeams of the plurality along at least a portion of the focus changingassembly 222. Each of the plurality of light beams may comprise asubstantially collimated configuration upon entering the focus changingassembly 222. The focus changing assembly 222 may similarly adjust eachof the plurality of light beams to a convergent configuration, asubstantially collimated configuration, or a divergent configurationupon exiting the focus changing assembly 222.

In the embodiment illustrated in FIG. 4, the focus changing assembly 220includes a variable optical power element 224. The variable opticalpower element 224 can be any suitable optical element having acontrollably variable optical power. For example, the variable opticalpower element 224 can include a variable power lens element or a liquidlens element, such as a liquid lens providing close focus ability andlower power consumption. The liquid lens may be electrically tunable tochange the optical power, such as by applying a suitable current (e.g.,within a range from 0 mA to 300 mA). In many embodiments, the variableoptical power element 224 includes a high refractive index material anda low refractive index material, and an interface between the materials(e.g., a meniscus) may be varied to adjust the optical power. Theoptical power of the variable optical power element 224 can be varied byany suitable amount, such as by approximately 2 diopters, 5 diopters, 10diopters, 15 diopters, 20 diopters, or 30 diopters. The optical power ofthe optical power element 224 can be varied over any suitable range,such as a range between any two of the following: 5 diopters, 8diopters, 10 diopters, 15 diopters, 16.5 diopters, 20 diopters, 22diopters, 25 diopters, or 50 diopters. The variable optical powerelement 224 can be operable to move the external focal plane 206 withoutmovement of the variable optical power element 224 (e.g., withoutmovement along the symmetry axis and/or without movement relative to theother components of the light focusing assembly 220). Accordingly, thelight focusing assembly 220 can provide scanning of the external focalplane 206 without any moving optical parts.

FIG. 5 illustrates another light focusing assembly 230, in accordancewith many embodiments, that can be included in the confocal optics 42.Similar to the light focusing assembly 220 illustrated in FIG. 4, thelight focusing assembly 230 includes an image space lens group 202, anobject space lens group 204, and a focus changing assembly 232, whichmay be disposed at a system aperture 208. The light focusing assembly230 may receive a plurality of light beams and overlap the light beamswithin the focus changing assembly 232, as described above. In the lightfocusing assembly 230, however, the focus changing assembly 232 includesa focus changing lens group 234 instead of a variable optical powerelement. The optical power of the focus changing lens group 234 can bevaried by relative movement between lens elements of the focus changinglens group 234. The relative movement between lens elements of the focuschanging lens group 234 can include displacing any suitable component ofthe focus changing group, such as a single lens element, multiple lenselements, one or more portions of a lens element, one or more portionsof multiple lens elements, or any suitable combination. For example, thefocus changing group can be a pair of lenses and the movement can be achange in separation between the lenses (e.g., along the symmetry axis).By varying the optical power of the focus changing lens group 234, theexternal focal plane 206 is displaced along the symmetry axis (e.g., tonear, intermediate, and far focus positions).

In the embodiment illustrated in FIG. 5, the focus changing lens group234 includes a convergent lens 236 (e.g., a biconvex lens) and adivergent lens 238 (e.g., a biconcave lens). The optical power of thefocus changing lens group 234 can be changed by varying the separationbetween the convergent lens 236 and the divergent lens 238. While thefocus changing lens group 234 is illustrated as having one convergentlens and one divergent lens, a suitable focus changing lens group caninclude any suitable combination of lens elements in which relativemovement between the lens elements effects a change in optical power.

In many embodiments, the movement of lens elements of the focus changinglens group 234 is small relative to the resulting displacement of theexternal focal plane 206. For example, an approximately 0 mm toapproximately 2 mm movement of the focusing changing lens group 234 mayproduce an approximately 15 mm movement of the external focal plane 206.The light focusing assembly 230 can be configured such that a change inseparation between lens elements of the focus changing lens group 234results in at least a 2-, 3-, 4-, 5-, 7.5-, or 10-fold larger change inseparation between the external focal plane 206 and the endoscopic probemember 46. In many embodiments, the displacement of the external focalplane 206 is approximately 2, 3, 4, 5, 7.5, or 10 times larger than thecorresponding change in separation between lens elements of the focuschanging lens group 234. The ratio of the movement distance of theexternal focal plane to the corresponding movement distance of theelements of the focusing changing assembly may be referred to herein asthe “movement gain factor.” The movement gain factor provided by thefocus changing assemblies may be approximately 1, 1.1, 2, 3, 4, 5, 7.5,10, or 15.

FIG. 6 is a simplified block diagram of acts of a method 300 fordetermining surface topography of a three-dimensional structure. Anysuitable optical assemblies, devices, apparatus, and/or systems, such assuitable embodiments described herein, can be used to practice themethod 300.

In act 310, a plurality of light beams is generated. Any suitable devicecan be used to produce the light beams. For example, referring to FIG.1A, the apparatus 20 can be used to produce the light beams. Theapparatus 20 can include the grating or micro lens array 38, whichsplits the laser beam 30 emitted by light source 28 into an array ofbeams 36.

In act 320, the light beams are overlapped within a focus changingassembly. For example, as with the light focusing assembly 220 and withthe light focusing assembly 230, the image space lens group 202 canoverlap the light beams onto the focus changing assembly 222 and 232,respectively. The focus changing assembly may be disposed at or near asystem aperture. Alternatively or in combination, the focus changingassembly may be situated at a back focal length of an objective lens orobject space lens group (e.g., a telecentric lens).

In act 330, the focus changing assembly is operated to move therespective external focal points of the light beams. In manyembodiments, the focus changing assembly includes a focus changing lensgroup or a variable optical power element disposed at a system aperture,for example, as in the light focusing assembly 220 or the light focusingassembly 230, respectively. In many embodiments, the external focalpoints form an external focal plane that can be displaced by varying theoptical power of the focus changing assembly. Referring to theendoscopic probe member 46 illustrated in FIG. 2B, in many embodiments,the light beams propagate along an optical path through the endoscopicprobe member 46 such that the external focal plane is disposed exteriorto the probe (e.g., focusing plane 100). The light beams emanate fromthe endoscopic probe member 46 at a location disposed between theexternal focal plane and the light focusing assembly (e.g., sensing face97). The optical path can be configured to generate an array ofilluminated spots on a structure being measured, as illustrated in FIG.1A by the illuminated spots 52 on the patient's teeth 26.

The external focal points can be displaced to scan the external focalplane through a plurality of focal depths. In many embodiments, thefocus changing assembly can be operated to vary the separation distancebetween the external focal points and the endoscopic probe member 46,such as by oscillating the separation distance through a specifiedrange. For example, the separation distance between the external focalpoints and the endoscopic probe member 46 can be oscillated by at least5 mm, at least 10 mm, at least 15 mm, or at least 20 mm. In manyembodiments, the oscillation of the separation distance can be within arange of approximately 10 mm to approximately 15 mm. Any suitableoscillation frequency can be used, such as a frequency greater than orequal to approximately 1 Hz, 10 Hz, 20 Hz, 50 Hz, 75 Hz, or 100 Hz. Theoscillation frequency may be within a range from approximately 10 Hz toapproximately 100 z, or approximately 50 Hz to approximately 100 Hz. Inembodiments that employ a focus changing assembly, such as in the lightfocusing assembly 220 and in the light focusing assembly 230, increasedoscillation rates may be achievable relative to the light focusingassembly 200 as a result of the reduced or eliminated movement of lightfocusing assembly components necessary to displace the external focalplane 206 through the desired distance.

In act 340, the characteristics of a plurality of light beams returningfrom the structure are measured. For example, as illustrated in FIG. 1A,the returning light beams 54 are reflected by the surface of thestructure and each correspond to one of the incident light beams 36produced by the optical device 22. Any suitable device can be used tomeasure the characteristics of the returning light beams, such as thesensor array 68. In many embodiments, the measured characteristic isintensity.

In act 350, data representative of topography of the structure isgenerated based on the measured characteristics, as previously describedherein. Any suitable device can be used to receive and generate thedata, such as the processor 24 depicted in FIG. 1B.

Table 1 provides an example configuration and operational parameters forthe light focusing assembly 200 (hereinafter “telescopic assembly”)illustrated in FIG. 3, the light focusing assembly 220 (hereinafter“variable element assembly”) illustrated in FIG. 4, and the lightfocusing assembly 230 (hereinafter “moving lens assembly”) illustratedin FIG. 5.

TABLE 1 Example configuration and operational parameters for lightfocusing assemblies. Telescopic Variable Element Moving Lens AssemblyAssembly Assembly External focal plane 15 mm  15 mm 15 mm movementdistance Focusing lens 15 mm 0  2 mm movement distance Optical powerchange N/A 5 N/A (diopter) Typical moving lens 50 grams N/A  5 gramsweight Movement gain factor 1 N/A 7.5 Maximum oscillation  1 Hz 100 Hz20 Hz frequency

For each of the three systems in Table 1, the external focal plane isdisplaced by 15 mm. In the telescopic assembly, a 15 mm movement of anobject space lens group weighing 50 g can be used to produce a 15 mmdisplacement of the external focal plane, for a movement gain factorof 1. The object space lens group can be oscillated at a maximumfrequency of approximately 1 Hz. In the variable element assembly, a 5diopter change in the optical power of a variable optical power lenselement without movement of any optical elements can be used to producea 15 mm displacement of the external focal plane. The optical power ofthe variable optical power element can be oscillated at maximumfrequency of approximately 100 Hz. In the moving lens assembly, a 2 mmmovement of a focus changing lens group moving lens that weighs 5 g canbe used to produce a 15 mm displacement of the external focal plane, fora movement gain factor of 7.5. The focus changing lens group can beoscillated at a maximum rate of approximately 20 Hz.

Notably, the variable element assembly and the moving lens assemblyprovide several advantages. With the variable element assembly and themoving lens assembly, the external focal plane may be displaceable withsignificantly smaller or no movement of optical focusing elements,respectively, when compared to the telescopic assembly. For the movinglens assembly, the weight of the moving optical element may besubstantially reduced compared to that of the telescopic assembly, thusreducing the amount of power needed to move the element. Furthermore,the maximum frequency of focal depth oscillation may be significantlyhigher for the variable element assembly and the moving lens assembly,thereby being compatible for use in systems with increased scanningrate, as compared to the telescopic assembly.

FIG. 7 illustrates an embodiment of a telescopic light focusing assembly400 similar to the telescopic light focusing assembly 200 illustrated inFIG. 3. In many embodiments, however, the telescopic light focusingassembly 400 may have a significant minimum unfold reach 402 (e.g., 80mm), which is the minimum distance between the front of the object spacelens group 404 and the external focal plane 406. The unfold reach 402may add to the overall length of the optical path between the grating ormicrolens array 38 and the structure being measured. It may, however, beadvantageous to reduce the length of the optical path between thegrating or microlens array 38 and the structure being measured toprovide a more compact optical device 22.

FIG. 8 illustrates an embodiment of a compact light focusing assembly410, in accordance with many embodiments. The compact light focusingassembly 410 can include a Z1 lens group 412 and a Z2 lens group 414. Afront end lens group 416 can be disposed along the optical path distalto the compact light focusing assembly 410. The Z1 lens group 412 andthe Z2 lens group 414 can be adjacently disposed. The Z2 lens group 414can be disposed between the Z1 lens group 412 and a system aperture 418.The system aperture 418 can be disposed between the Z2 lens group 414and the front end lens group 416, such as at a back focal length of thefront end lens group 416. The Z1 and Z2 lens groups 412, 414 may beconfigured to overlap a plurality of light beams toward the systemaperture 418. The Z1 and Z2 lens groups 412, 414 may adjust theconfiguration of light beams passing through the system aperture 418,such as by converging, diverging, or substantially collimating the lightbeams.

The Z1 lens group 412 and the Z2 lens group 414 can include any suitablelens or combination of lenses. For example, the Z1 lens group 412 caninclude a convergent lens (e.g., a biconvex lens) and the Z2 lens group414 can include a divergent lens (e.g., a biconvex lens). The front endlens group 416 can include any suitable lens or combination of lenses,such as a convergent lens (e.g., a plano-convex lens with the planarface disposed towards the external focal plane 406). One or more of theZ1 lens group 412, Z2 lens group 414, or front end lens group 416 mayinclude a telecentric lens. For example, in many embodiments, the frontend lens group 416 is a telecentric lens. In the illustrated embodiment,an unfolded reach 420 (e.g., 110 mm in the intermediate focus position)between the distal face of the Z2 lens group 414 and the external focalplane 416 results in a reduced optical path length between the gratingor microlens array 38 and the structure being measured. In both thetelescopic light focusing assembly 400 and the compact light focusingassembly 410, the unfold reach can be measured from the distal face of alens group that is moved so as to displace the location of the externalfocal plane 406.

In the compact light focusing assembly 410, the external focal plane 406can be displaced along the symmetry axis by varying the separationbetween the Z1 lens group 412 and the Z2 lens group 414. Varying theseparation between the Z1 lens group 412 and the Z2 lens group 414 canbe accomplished by moving the Z1 lens group 412, moving the Z2 lensgroup 414, or moving both the Z1 lens group 412 and the 9Z2 lens group414. For example, the separation between a convergent and divergent lenscan be increased to vary the external focal plane between far,intermediate, and near focus positions.

FIG. 9 illustrates an optical assembly 430 that includes the compactlight focusing assembly 410 and a probe 432 in accordance with manyembodiments. The light beams focused by the compact light focusingassembly 410 can enter the probe 432 through a face 434 disposed towardsthe system aperture 418, reflect off the walls of the probe, and emanatefrom a face 436 disposed towards the external focal plane 406. The probe432 can be manufactured from any suitable material, such as a lighttransmissive material (e.g., glass). In many embodiments, the walls ofthe probe are totally reflective, such that light beams reflect off theinternal walls of the probe as they propagate through the probe. Theprobe can be probing member 90, as illustrated in FIGS. 2A and 2B. Inmany embodiments, a thin lens is positioned at a probe exit aperture436.

The external focal plane 406 can be displaced relative to the probe 432along the direction of the light beams emanating from the probe. Theexternal focal plane 406 can be displaced by varying the separationbetween the Z1 lens group 412 and the Z2 lens group 414, as describedabove.

In many embodiments, a change in the distance between the Z1 and Z2 lensgroups produces a larger change in the distance between the probe 432and the external focal plane 406. For example, the compact lightfocusing assembly 410 can be configured such that a change in thedistance between the Z1 lens group 412 and the Z2 lens group 414produces at least a 2-fold larger change in the separation between theprobe 432 and the external focal plane 406. In many embodiments, thecompact light focusing assembly 410 is configured such that a change inthe distance between the Z1 lens group 412 and the Z2 lens group 414produces at least a 4-fold larger change in the separation between theprobe 432 and the external focal plane 406. FIGS. 8 and 9 illustratesimilar concepts, with FIG. 9 having the probe added to demonstratesuitability to a very slim probe. FIG. 8 illustrates the optical extentthat would be required without the use of the forward aperture concept.

Use of the compact light focusing assembly 410 may result in significantreduction in overall optical path length. The compact light focusingassembly 410 may provide a reduced optical path length (as compared toexisting approaches) without compromising field of view (FOV).

FIG. 10 illustrates acts of a method 500 for determining surfacetopography of a three-dimensional structure, in accordance with manyembodiments. Any suitable optical assemblies, devices, apparatus, and/orsystems, such as suitable embodiments described herein, can be used topractice the method 500.

In act 510, a plurality of light beams is generated. Any suitable devicecan be used to produce the light beams. For example, referring to FIG.1A, the apparatus 20 can be used to produce the light beams. Theapparatus 20 includes the grating or micro lens array 38, which splitsthe laser beam 30 emitted by light source 28 into an array of beams 36.

In act 520, the light beams are propagated through a convergent lens, adivergent lens, and a probe. Any suitable optics can be used toaccomplish act 520. For example, the embodiments illustrated in FIG. 8and FIG. 9 can be used to accomplish act 520.

In act 530, the separation between the convergent lens and the divergentlens is varied to vary the separation between the probe and therespective external focal points of the light beams. Referring, forexample, to the embodiments illustrated in FIG. 9, the external focalpoints can form an external focal plane located exterior to the probe.The separation between the probe and the external focal plane can beincreased by decreasing the separation between the convergent anddivergent lenses. In some instances, the separation between the probeand the external focal points can be varied to scan the external focalplane through a plurality of focal depths. The separation can beoscillated by a suitable distance and at a suitable frequency, such asby the values previously provided herein with respect to the method 300.For example, the distance between the convergent and divergent lensescan be varied symmetrically by 1 mm, resulting in a 10 mm external focalplane shift.

In act 540, characteristics of the respective light beams returning fromthe respective light spots are measured. For example, as illustrated inFIG. 1A, the returning light beams 54 are reflected by the surface ofthe structure and each correspond to one of the incident light beams 36produced by the optical device 22. Any suitable device can be used tomeasure the characteristics of the returning light beams, such as thesensor array 68.

In act 550, data representative of topography of the structure isgenerated based on the measured characteristics, as previously describedherein. Any suitable device can be used to receive and generate thedata, such as the processor 24 depicted in FIG. 1B.

Any suitable features of any of the embodiments of the assemblies,systems, methods, and devices described herein can be combined orsubstituted with any suitable features of other embodiments describedherein. For example, the confocal optics 42 of the optical device 22 caninclude any of the light focusing assemblies described herein, such asany of the light focusing assemblies 220, 230, 410. In many instances,the exemplary optical systems described herein can be combined with aprobe, such as the probing member 90, to facilitate optical measurementof the intraoral cavity. One of skill in the art will appreciate thereare many suitable combinations and substitutions that can be made fromthe systems, methods, and devices described herein.

While preferred embodiments of the present invention have been shown anddescribed herein, it will be obvious to those skilled in the art thatsuch embodiments are provided by way of example only. Numerousvariations, changes, and substitutions will now occur to those skilledin the art without departing from the invention. It should be understoodthat various alternatives to the embodiments of the invention describedherein may be employed in practicing the invention. It is intended thatthe following claims define the scope of the invention and that methodsand structures within the scope of these claims and their equivalents becovered thereby.

1. (canceled)
 2. An apparatus for determining surface topography of astructure, the apparatus comprising: an illumination unit configured tooutput a plurality of light beams; a light focusing assembly comprisingan image space lens, an object space lens and a focus changing assemblybetween the image space lens and the object space lens and beingconfigured to: overlap the plurality of light beams within the lightfocusing assembly; and focus each of the plurality of light beams to aplurality of external focal planes to generate illuminated spots on thestructure a detector configured to measure a characteristic a pluralityof light beams returning from the illuminated spots on the structure;and a processor coupled to the detector and configured to generate datarepresentative of topography of the structure based on the measuredcharacteristic of each of the plurality of reflected light beams.
 3. Theapparatus of claim 2, wherein at least a portion of the focus changingassembly is located at a back focal length of an objective lens.
 4. Theapparatus of claim 2, wherein the focus changing assembly is locatedalong optical paths of the plurality of light beams such that one ormore of the plurality of light beams overlaps with one or more otherlight beams of the plurality of light beams along at least a portion ofthe focus changing assembly.
 5. The apparatus of claim 2, wherein eachof the plurality of light beams are substantially collimated uponentering the focus changing assembly and wherein the focus changingassembly adjusts each of the plurality of light beams to a convergentconfiguration, a collimated configuration, or a divergent configurationupon exiting the focus changing assembly.
 6. The apparatus of claim 2,wherein the characteristic comprises an intensity of the reflected lightbeams.
 7. The apparatus of claim 2, wherein the focus changing assemblymoves the plurality of external focal planes at least 10 mm.
 8. Theapparatus of claim 2, wherein the object space lens comprises atelecentric lens and at least a portion of the focus changing assemblyis located at a back focal length of the telecentric lens.
 9. Theapparatus of claim 2, wherein the image space lens comprises a focallength and location arranged to overlap and substantially collimate theplurality of light beams passing through the focus changing assembly.10. The apparatus of claim 2, wherein the focus changing assemblycomprises the variable optical power element and is operable to move therespective focal points without movement of the variable optical powerelement, thereby oscillating separation between the respective focalpoints and the probe by at least 10 mm at a frequency greater than 10Hz.
 11. The apparatus of claim 2, wherein the focus changing assemblycomprises the divergent lens and the convergent lens, and separationbetween the divergent lens and the convergent lens is varied to displacethe external focal points.
 12. A method of determining surfacetopography of a structure, the method comprising: illuminating thestructure using a light focusing assembly including an image space lens,an object space lens, and a light focusing assembly between the imagespace lens and the object space lens to overlap each of the plurality oflight beams within the light focusing assembly and focus each of aplurality of light beams to a plurality of external focal planes toilluminate the structure; a portion of the focus changing assemblylocated at a back focal length of the object space lens and comprising avariable optical power element or a divergent and a convergent lens;operating the focus changing assembly to displace the respective focalpoints to the plurality of external focal planes; measuring acharacteristic of each of a plurality of light beams returning from theilluminated structure; and generating, with a processor, datarepresentative of topography of the structure based on the measuredcharacteristic.
 13. The method of claim 12, wherein at least a portionof the focus changing assembly is located at a back focal length of anobjective lens of the light focusing.
 14. The method of claim 12,wherein the focus changing assembly is located along optical paths ofthe plurality of light beams such that one or more of the plurality oflight beams overlaps with one or more other light beams of the pluralityof light beams along at least a portion of the focus changing assembly.15. The method of claim 12, wherein each of the plurality of light beamsare substantially collimated upon entering the focus changing assemblyand wherein the focus changing assembly adjusts each of the plurality oflight beams to a convergent configuration, a collimated configuration,or a divergent configuration upon exiting the focus changing assembly.16. The method of claim 12, wherein the characteristic comprises anintensity of the returning light beams.
 17. The method of claim 12,wherein the focus changing assembly moves the plurality of externalfocal planes at least 10 mm.
 18. The method of claim 12, wherein theobject space lens comprises a telecentric lens and at least a portion ofthe focus changing assembly is located at a back focal length of thetelecentric lens.
 19. The method of claim 12, wherein the image spacelens comprises a focal length and location arranged to overlap andsubstantially collimate the plurality of light beams passing through thefocus changing assembly.
 20. The method of claim 12, wherein the focuschanging assembly comprises the variable optical power element operableto move the focal plane without movement of the variable optical powerelement, thereby oscillating separation between the respective focalpoints and the probe by at least 10 mm at a frequency greater than 10Hz.
 21. The method of claim 12, wherein the focus changing assemblycomprises the divergent lens and the convergent lens, and separationbetween the divergent lens and the convergent lens is varied to displacethe external focal points.